Currently, there exist anti-lock braking devices for vehicles, popularly known as ABS, which act on brakes of the type that comprise friction elements secured to the vehicle, usually brake pads mounted on the corresponding vehicle sleeve or bushing by means of calipers; these friction elements actuate frictional tracks secured to the wheels—usually brake discs—, and are actuated by means of a primary hydraulic circuit that is controlled by the brake pedal whilst driving, very often with the aid of an intensifier or assistant that amplifies the pressure implemented on the pedal such that the braking pressure exerted by the friction elements is capable of performing effective braking without requiring excessive force on the pedal.
The action of this type of assisted braking is sometimes so potent that it may cause one or more wheels to lock up, especially on low-grip surfaces or in limit brakings. This situation reduces safety, since, except in the case of dry, optimal-grip surfaces and other situations, such as newly-fallen snow that may accumulate in front of the wheels when braking, the sliding increases the car stopping distance, thereby increasing the risk of collision, and, no less significantly, decreases vehicle stability, due to the loss of directional capabilities caused by the front wheels (which are those primarily responsible for braking) losing grip or to the displacement of the rear part of the vehicle caused by the rear wheels losing grip, or to both effects simultaneously.
Precisely in order to solve this problem, anti-lock braking systems were designed that currently operate exclusively with electronic regulation, wherein sensors placed on the wheels (currently one on each wheel, although the early versions of these systems implemented sensors only for the rear axle) take continuous measurements (several times per second) of the wheel rotation speed, and send them to a control unit, which, if it detects a deceleration greater than certain pre-determined limits for effective braking, actuates solenoid valves inserted in the corresponding primary hydraulic circuit of each wheel, such that they open and release the braking pressure, thereby causing the wheel to recover its grip. As in the case of the sensor readings, the action of these valves is performed several times per second, which is noticed in the brake pedal as a clicking sound.
These electronically-regulated systems have various disadvantages, which include:
The sensors used are capacitive sensors, which are designed to prevent wearing elements, but nonetheless undergo changes in operation and failures due to temperature changes and hysteresis that may affect the correct operation of the system.
The electronic elements used are susceptible to electrical failures, even more so in environments with high static electricity, such as a moving vehicle supported on the ground by means of electrically-insulated tyres.
It is a very intrusive system, which is clearly perceptible to the drivers without them being capable of acting on it.
Since it is an electronic aid, its use in competitions, such as car races (Formula 1®), is not permitted.